Re: [PATCH] hw/core/loader: Fix possible crash in rom_copy()

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Sep 25, 2019 at 03:03:31PM +0200, Thomas Huth wrote:
> Both, "rom->addr" and "addr" are derived from the binary image
> that can be loaded with the "-kernel" paramer. The code in
> rom_copy() then calculates:
> 
>     d = dest + (rom->addr - addr);
> 
> and uses "d" as destination in a memcpy() some lines later. Now with
> bad kernel images, it is possible that rom->addr is smaller than addr,
> thus "rom->addr - addr" gets negative and the memcpy() then tries to
> copy contents from the image to a bad memory location. In the best case,
> this just crashes QEMU, in the worst case, this could maybe be used to
> inject code from the kernel image into the QEMU binary, so we better fix
> it with an additional sanity check here.
> 
> Cc: qemu-stable@nongnu.org
> Reported-by: Guangming Liu
> Buglink: https://bugs.launchpad.net/qemu/+bug/1844635
> Signed-off-by: Thomas Huth <thuth@redhat.com>

Reviewed-by: Michael S. Tsirkin <mst@redhat.com>

> ---
>  hw/core/loader.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/core/loader.c b/hw/core/loader.c
> index 0d60219364..5099f27dc8 100644
> --- a/hw/core/loader.c
> +++ b/hw/core/loader.c
> @@ -1281,7 +1281,7 @@ int rom_copy(uint8_t *dest, hwaddr addr, size_t size)
>          if (rom->addr + rom->romsize < addr) {
>              continue;
>          }
> -        if (rom->addr > end) {
> +        if (rom->addr > end || rom->addr < addr) {
>              break;
>          }
>  
> -- 
> 2.18.1